The technique of nuclear magnetic resonance (NMR) will be utilized to correlate changes in reabsorptive transport by the isolated perfused rat kidney with changes in the tissue content of high-energy organic phosphate compounds. The techniques of enzymatic analysis of metabolic intermediates in snap-frozen tissue and in kidney perfusate will also be employed. The information developed should permit inferences about the tightness of coupling between transport, ATP and phosphorylation potential in the intact kidney.